Abstract
Thermoluminescence (TL) of large grain (10 μm) polycrystalline calcium sulfide prepared by the “sulfurising flux” method was compared with that of small grain agglomerated material prepared by the “nonflux” method. The TL spectrum is of much reduced intensity indicating an appreciable reduction in the density of trap-inducing defects in large grain CaS. The main feature of TL above room temperature is a peak at about 470 K found only in one sample with Ce concentration of 0.001 mole fraction. This peak anneals above about 300°C (573 K) and is sensitive to X-ray irradiation in a manner which may be of interest in radiation dosimetry. An analysis made of TL yields values for trap depth E of 1.42±0.05 eV and escape frequency factor S of 1.64×10 14 s -1. It also appears from the analysis that luminescence is thermally quenched in this temperature region. This trap appears likely to be an electron trap formed by an aggregate of positive ions, one of which is an F 1+ centre due to a sulfur vacancy with one permanently trapped electron.
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